1. Field of the Invention
This invention relates to a low temperature ethylene oligomerization process for preparing linear alpha-olefins having a narrow molecular weight distribution, in the presence of a catalyst system comprising (1) titanium halide (2) organoaluminum halide and (3) a halogenated phosphorus compound.
2. Description of the Prior Art
It is known to prepare olefins by "ethylene growth", wax cracking and n-paraffin dehydrogenation. However, wax cracking and dehydrogenation result in low yields and poor quality of specific alpha-olefins.
A more widely used process based on "ethylene growth" (Ziegler) technology utilizes triethylaluminum at elevated pressures (e.g., 1500 psi) and high temperatures (ca. 200.degree.C). A drawback of this process is the wide range (C.sub.4 -C.sub.30 +) of olefins produced with product maximization about C.sub.12 -C.sub.14.
U.S. Pat. No. 3,574,782 and U.S. Pat. No. 3,652,705 disclose catalytic, low temperature (ca. -30.degree. to +80.degree.C) ethylene oligomerization based on titanium and alkyl aluminum catalysts. More specifically, U.S. Pat. No. 3,574,782 is directed to titanium-aluminum catalysts modified by a phosphine or phosphite and U.S. Pat. No. 3,652,705 is directed to titanium-aluminum catalysts modified by tertiary phosphines, ketones, esters, nitriles, ethers, amines and organic sulfur compounds.